Molybdenum plays an essential role in the metalloenzyme, nitrogenase, the dinitrogen fixing system of microorganisms. Although there is little direct evidence as to the nature of the metal-binding site, it has been suggested that N2 is coordinated and held at this reducing center during the electron transfer process. Consideration of known compounds of molybdenum supports metal bonding to oxygen and sulfur donors. A major objective of the proposed research is to provide new chemical and structural information about molybdenum-sulfur complexes. Synthetic efforts will be directed toward the preparation of mercapto, sulfido and oxobridged molybdenum dimers, since chromophores of this type may be important functional units at the active site of nitrogenase enzymes. Chelating, and multidentate sulfur ligands, including sulfur-containing amino-acids, will be investigated in an effort to define structural trends. The molecular geometry and the electrochemical behavior of these species will be investigated with a view to providing new data from which chemists interested in the nitrogenase system may draw. In addition, the reactions of these species and a variety of molybdenum compounds with nitrogen containing ligands will be investigated to provide structural types with molybdenum-nitrogen multiple bonds, a structural situation analogous to possible intermediate steps in dinitrogen fixation.